The present invention relates to a microwave plane antenna formed from a number of radiating elements (receivers or, according to the principle of reciprocity of antennas, transmitters), having at least one system of planar lines placed on a sheet of dielectric of "completely suspended substrate lines' type enclosed between devices at least locally metallic or metallized in which cut-outs placed facing each other are bored in order to form elementary open or closed waveguides. The ends of the central conductors of the planar lines are placed inside these waveguides in order to form probes which produce a coupling enabling the reception (or transmission) of microwave signals. Studs are provided to hold the sheet of dielectric at a certain distance from the said devices.
The present invention also relates to a method of manufacturing a component of the antenna.
Such antennas are used in particular for receiving satellite television transmissions at a frequency of about 12 GHz.
A microwave plane antenna including an assembly of such elements has been described in French patent application No. 2544920, corresponding to U.S. Pat. No. 4,614,947. In it there is in particular described an arrangement enabling the transmission lines forming the antenna feed system or systems to be supported. Each of the systems of microwave lines is formed by a printed circuit deposited on a thin sheet of dielectric serving as a substrate enclosed between two metallic plates or between two metallized dielectric plates. Each system is placed in such a way that the ends of the central conductors of the lines are facing square cut-outs bored in each of the plates which enclose it respectively in order to produce the coupling between the lines and the cut-outs. Each sheet of dielectric carrying the system of printed central conductors of the microwave lines is supported between the plates which enclose it by positioning studs located on the surfaces of these plates, facing each other and on either side of this sheet, these studs also being placed, with respect to this sheet, in spaces having no printed circuits.
Such an antenna has the disadvantage that the plates, forming both the main framework of the antenna and the waveguide system, must be very rigid and have high dimensional accuracy. Metal plates with such a complex structure are expensive and also very heavy. Plates made from metallized plastic material have heat expansion characteristics that are not appropriate for the production of a large-sized antenna which must operate equally well at -40.degree. as in the summer sunshine.